Conventionally, there has been proposed a display device with a photosensor that, due to including a photodetection element such as a photodiode inside a pixel, can detect the brightness of external light and pick up an image of an object that has come close to the display. Such a display device with a photosensor is envisioned to be used as a bidirectional communication display device or display device with a touch panel function.
In a conventional display device with a photosensor, when using a semiconductor process to form known constituent elements such as signal lines, scan lines, TFTs (Thin Film Transistors), and pixel electrodes on an active matrix substrate, photodiodes or the like are formed at the same time on the active matrix substrate (e.g., see PTL 1).
FIG. 25 shows an example of a conventional photosensor (e.g., see PTL 2 and 3) formed on an active matrix substrate. The conventional photosensor shown in FIG. 25 is configured by a photodiode D1, a capacitor C2, and a transistor M2. The anode of the photodiode D1 is connected to wiring for supplying a reset signal RS. The cathode of the photodiode D1 is connected to one of the electrodes of the capacitor C2 and the gate of the transistor M2. The drain of the transistor M2 is connected to wiring for supplying a constant voltage Vsup. Note that sensor circuit output data SData of the photosensor is output from the source of the transistor M2. The other electrode of the capacitor C2 is connected to wiring for supplying a readout signal RW.
In this configuration, sensor circuit output data SData that is in correspondence with the amount of light received by the photodiode D1 can be obtained by supplying the reset signal RS and the readout signal RW in accordance with respective predetermined timings. Next is a description of the operation of the conventional photosensor shown in FIG. 25, with reference to FIG. 26. Note that in FIG. 26, the low level (e.g., −4 V) of the reset signal RS is indicated as −Vb, and the high level (e.g., 8 V) of the readout signal RW is indicated as Vrw. It should also be noted that the high level of the reset signal RS is considered to be 0 V, and the low level of the readout signal RW is considered to be 0 V.
A sensing sequence of the photosensor shown in FIG. 25 is described below in three parts, namely (A) readout period, (B) reset period, and (C) sensing period.
(A) Readout Period
The readout period corresponds to the period in which the readout signal RW is at the high level. While the readout signal RW is at the high level, the potential VINE of a storage node is “pulled up” via the capacitor C2. Note that the storage node is a connection point between the capacitor C2, the cathode of the photodiode D1, and the gate of the transistor M2. At this time, letting the storage node potential immediately before readout be V0, the capacitance of the capacitor C2 be Cst, the total in-circuit capacitance be Ctotal, and the amplitude of the readout signal RW be Vrw, the potential VINT of the storage node can be obtained by the below expression.VINT=Cst/CtotalVrw+V0 
Then, due to the “pulled-up” potential VINE exceeding the threshold value of the transistor M2, the transistor M2 is turned on, and the sensor data SData is output. At this time, letting the threshold value of the transistor M2 be Vth, the current value of a constant current source be I, and the conductance of the transistor M2 be β, the potential Vout of SData can be obtained by the below expression.Vout≈VINT−Vth(2I/β)1/2 
(B) Reset Period
Due to the reset signal RS rising to the high level (0 V), a forward current flows to the photodiode D1, and the potential VINT of the storage node is reset to 0 V.
(C) Sensing Period
The sensing period starts when the reset signal has returned from the high level to the low level. In other words, after the storage node has been reset in the reset period as mentioned above, the reset signal RS falls to the low level (−Vb), and thus the photodiode D1 becomes reverse biased. Then, the storage node changes to the −Vb direction due to a photocurrent that is in accordance with the amount of light that has been incident on the photodiode D1.
The above-described (A) readout period, (B) reset period, and (C) sensing period are considered to be one cycle, and sensor data is read out from the photosensor by repeatedly performing this cycle.
FIG. 27 shows an example of a configuration of a photosensor inside a pixel. In the exemplary configuration shown in FIG. 27, one sensor circuit 81 is provided in each pixel configured by three colors of picture elements, namely red (r), green (g), and blue (b). Among the constituent elements shown in FIG. 25, the sensor circuit 81 corresponds to the photodiode D1, the capacitor C2, and the transistor M2. In the example in FIG. 27, gate lines GL and source lines SL are arranged in a matrix, and TFTs 83 for driving pixel electrodes 82r, 82g, and 82b of the picture elements are arranged at intersections between the gate lines GL and the source lines SL. The gates of the TFTs 83 are connected to the gate lines GL, the sources thereof are connected to the source lines SL, and the drains thereof are connected to the pixel electrodes 82r, 82g, and 82b. Note that in the example in FIG. 27, the three pixel electrodes 82r, 82g, and 82b make up one unit, and are repeatedly disposed along the row direction.
The number of gate lines GL provided on the matrix substrate is L. In other words, the number of pixels on the matrix substrate in the row direction is L. The gate lines GL are indicated as GL(l) (l is a natural number from 1 to L) when there is a need to distinguish between individual gate lines GL. Source lines SLr, SLg, and SLb make up one set of source lines SL, and M sets (i.e., 3M lines) are provided on the matrix substrate. In other words, the number of pixels on the matrix substrate in the column direction (horizontal direction) is M, and the number of picture elements in the column direction is 3M. Hereinafter, the source lines SL are indicated as SLr(m), SLg(m), and SLb(m) when there is a need to distinguish between individual source lines SL. Specifically, m is a natural number from 1 to M.
Note that N wiring lines for supplying the above-described reset signal RS and readout signal RW to the sensor circuits 81 are provided as a control signal line group RCTL for driving the sensor circuits 81. Note that there are cases where N is equal to L, which is the number of gate lines GL, and cases where N is less than L. For example, in a configuration in which the sensor circuit 81 is provided in all pixels in the row direction (vertical direction), N is equal to L, and in the example where the sensor circuit 81 is provided in every other pixel in the row direction, N is equal to L/2.
Also, in the example in FIG. 27, a power supply line Vsup that supplies power to the sensor circuit 81 is provided between the source lines SLg(m) and SLb(m). Furthermore, output wiring SData for outputting data from the sensor circuit 81 is provided between the source lines SLr(m) and SLg(m).
A configuration is also possible in which, as shown in FIG. 28, any of the source lines SL (in the example in FIG. 28, SLr(m) and SLg(m)) also serve as the power supply line Vsup and the output wiring SData. In this configuration, although there is a constraint in terms of timing in that sensor driving needs to be executed in a period in which the source lines SL are not used in a video display operation (e.g., the blanking period), there is the advantage of having a high pixel aperture ratio since the number of wiring lines is reduced. Specifically, in the configuration shown in FIG. 28, a video signal is applied to the source lines SL while a video display operation is performed. On the other hand, during sensor driving (e.g., the blanking period), a switch is switched to cause a constant voltage to be supplied from the power supply to the source line SLg(m), thus causing this source line to function as the power supply line Vsup. Similarly, a switch is switched to cause sensor circuit output data to be output from the sensor circuit 81 to the source line SLr(m). Accordingly, this source line functions as the output wiring SData during sensor driving.